The field of the invention is systems and methods for medical imaging. More particularly, the invention relates to systems and methods for improving fidelity of contrast dynamics in medical imaging modalities including diagnostic computed tomography, x-ray C-arm imaging, x-ray tomosynthesis imaging, ultrasound imaging, optical imaging, and magnetic resonance imaging.
The outcome of managing ischemic stroke critically depends on the time spent on diagnosis and interventions. To identify salvageable tissues of stroke patients, either x-ray computed tomography (“CT”) perfusion or magnetic resonance imaging (“MRI”) perfusion imaging is commonly ordered. Unfortunately, it often takes hours to schedule and perform perfusion imaging studies. The transportation of diagnostic patients between the imaging and interventional suites not only adds burden to work flow, but it also increases treatment time in the already very tight time window for stroke treatment, which is usually within six hours from onset of the stroke.
Image-guided interventions are normally conducted in an angiographic suite; thus, if the perfusion information can be obtained with an angiographic C-arm cone beam CT (“CBCT”) system, the stroke patients may be directly triaged to the angiographic suite to minimize the diagnostic time before interventions. It would therefore be desirable to be able to perform perfusion imaging with a C-arm CBCT system.
Flat-panel detector based C-arm CBCT systems, however, are significantly different from sub-second rotation, slip-ring gantry based diagnostic CT systems. C-arm CBCT has a prolonged data acquisition time that is limited by detector readout speed, mechanical stability of the C-arm gantry, and radiation safety requirements. As a result, typically less than ten time frames can be acquired within a minute of data acquisition time. For each time frame, the temporal resolution is limited to 3-5 seconds. Therefore, there are two major challenges in current attempts to achieving C-arm cone-beam CT perfusion. First, temporal resolution of 3-5 seconds is too poor to accurately record and delineate contrast dynamics. Second, the total number of acquired time frames is too few to enable estimation of perfusion information from time density curves. In addition to future hardware upgrades that may enable faster data acquisitions using the C-arm gantry, it would be highly desirable to develop technology that would enable perfusion imaging using the current hardware acquisition systems.
An interleaved scan method was proposed to improve the perfusion performance of C-arm CBCT systems. In this method, two perfusion scans are performed, with the second perfusion scan having a different x-ray delay time after contrast injection. For example, the contrast injection in the second scan may be delayed by three seconds relative to the first scan. Assuming the contrast dynamics are identical with the same contrast injection protocol, the available time frames can be doubled with this method.
There are limitations for the interleaved CBCT perfusion image method, however. First, the assumption made by this method—that contrast dynamics are repeatable in cerebral perfusion studies—has never been validated. Second, because two perfusion scans are required, both the contrast dose and the radiation dose are doubled. In addition, the data acquisition time are also doubled. None of these increases are desirable for improved patient care. Another limitation of the interleaved method is that the temporal resolution of each time frame is still the same as with conventional methods, even though the available time frames are doubled. Thus, the interleaved method only partially addresses the temporal sampling problems of C-arm CBCT perfusion imaging and does not address the temporal resolution problems.
It would therefore be desirable to provide systems and methods for medical imaging in which the fidelity of contrast dynamics and kinematics is enhanced relative to currently available technologies.